1. Field of the Invention
This invention relates to laser systems in which cylindrical lenses couple the outputs of laser diodes into optical fiber waveguides to provide pump light for lasing action in laser cavities and particularly to cylindrical lenses for coupling light from laser diode arrays into optical fiber waveguides.
2. Background of the Prior Art
Various means have been used to couple light from arrays of aligned laser diode stripes into optical fiber waveguide ends for the purpose of pumping solid state lasers. U.S. Pat. Nos. 4,818,062, 4,479,224, 4,383,318, and 4,911,526 disclose butt coupling light from laser diode arrays into optical fiber waveguide ends by placing the emitting faces of the laser diodes as close as possible to the entrance faces of the optical fiber waveguides. However, butt coupling makes it difficult to achieve high coupling efficiency because of the large angular divergences of laser diode stripes, at least in one azimuth, compared with the numerical aperture of the optical fiber waveguide in the same azimuth. Efficient coupling in these circumstances also requires critical close spacing and alignment of the members and/or fiber cladding having very low refractive indices. The close spacing also risks damage to the members.
U.S. Pat. No. 4,972,427 discloses coupling of laser diodes in a laser bar into a slab of a Talbot cavity using a lenticular array aligned with the diodes and a cylindrical lens behind the lenticular array. This passes light into the slab but apparently does not simplify attainment of greater efficiencies.
U.S. Pat. No. 5,127,068 discloses coupling the output of laser diodes into optical fiber waveguides by collimating the output emissions of the laser diodes with a cylindrical optical fiber having a diameter roughly equal to the diameter of the optical fiber waveguides to be coupled to and preferably 20% to 50% larger than the lateral dimension of the laser diode emitter regions. The patent discloses spacing the optical fiber end from the microlens as closely as possible and also suggests that cross-sections such as elliptical and hyperbolic could be useful for correction of particular spherical aberrations.
However, no matter how close one places such fiber waveguides to such a collimating lens, off axis rays may still fall outside the acceptance angle of the fiber waveguides. Moreover, cylindrical fiber lenses with round or other conic cross-sections may correct well on-axis but quickly degrade off-axis. This affects coupling efficiency adversely.
U.S. Pat. No. 4,826,269 discloses focusing diode lasers onto a single region by circularly disposing a number of vertical and horizontal cylindrical lenses. The complexity of such a device makes it unsuitable for many applications.
U.S. Pat. No. 5,081,639 discloses a method of making a cylindrical microlens which produces focused, defocused, or collimated exiting light and having circular, elliptical, and hyperbolic cross-sectional shapes. Such lenses are also well-corrected on-axis but rapidly degrade off-axis. Thus, they have limited ability to couple light simply and efficiently from laser diodes into fiber waveguides.
Furthermore, such small-fiber cylindrical lenses tend to sag. This makes it difficult to align them with the diodes and the optical fiber ends.
An object of this invention is to avoid these disadvantages.
Another object is to improve laser systems.
Another object of the invention is to improve coupling of light from laser diodes to optical fiber waveguides.
Yet another object of the invention is to furnish cylindrical lenses for efficient coupling of light from laser diodes into optical fiber waveguides.
Still another object of the invention is to improve manufacturing methods and means for such cylindrical lenses.
Yet another object of the invention is to improve systems for generating light for pumping solid state lasers.
Other objects of the invention will, in part, appear hereinafter and, in part, be obvious when the following detailed description is read.